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Numéro de publicationUS6178177 B1
Type de publicationOctroi
Numéro de demandeUS 08/811,246
Date de publication23 janv. 2001
Date de dépôt3 mars 1997
Date de priorité27 févr. 1997
État de paiement des fraisCaduc
Autre référence de publicationDE69830531D1, DE69830531T2, EP0866583A1, EP0866583B1
Numéro de publication08811246, 811246, US 6178177 B1, US 6178177B1, US-B1-6178177, US6178177 B1, US6178177B1
InventeursBernard Vautey
Cessionnaire d'origineAlcatel
Exporter la citationBiBTeX, EndNote, RefMan
Liens externes: USPTO, Cession USPTO, Espacenet
Data-processing network having non-deterministic access, but having deterministic access time
US 6178177 B1
Résumé
A network includes stations that communicate with one another via a common medium using a non-deterministic protocol. The risk of collision between the two frames transmitted simultaneously by two stations is reduced by providing each station with a detector to determine whether there is a risk of collision based on counter updates for recent transmissions performed by the station. Each station further includes a delay to limit a station's means bit rate to a predetermined maximum value when there is a risk of collision of data sent by the stations on the network. The maximum bit rate is chosen such that the sum of the values for all of the stations is less than the mean bit rate that can be accommodated by the common medium.
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Revendications(8)
What is claimed is:
1. A data-processing network having non-deterministic access but having a deterministic access time, the network including a plurality of stations communicating with one another by accessing a common medium using a non-deterministic protocol, wherein each respective one of said plurality of stations includes:
means for detecting whether there is a risk of collision between two or more of the plurality of stations trying to access the common medium; and
a means for limiting a mean bit rate of the station over the common medium to a predetermined maximum value at least during periods in which there is a risk of collision between a plurality of stations trying to access the common medium, said maximum value being chosen such that a sum of the maximum values chosen for all of the stations is less than a mean bit rate that can be accommodated by the common medium.
2. A network according to claim 1, wherein the means for limiting the mean bit rate of the respective station comprise time-delay means authorizing a station to access the common medium after expiration of a delay, said delay starting at an end of a most recent access by the station, and said delay having a duration which is proportional to a duration of said most recent access.
3. A network according to claim 1, wherein the means for detecting whether there is a risk of collision between the plurality of stations comprises, means for determining whether at least one collision has taken place since a beginning of the most recent transmission performed by the station over the common medium, and for concluding that there is a risk of collision if at least one collision has occurred since the end of the most recent transmission performed by said station.
4. A data processing network including a plurality of stations communicating with each other by accessing a common medium using a non-deterministic protocol, each one of said plurality of stations including:
a collision counter to detect a number of collisions on the common medium;
a time delay counter receiving a clock signal, said time delay counter including a decrementing circuit;
a register storing an authorization flag; and
a processor interconnecting the time delay counter, register, and collision counter, the processor receiving an output of the time delay counter and a count value of the collision counter to set a state of the authorization flag in the register,
wherein said processor determines authorization access of the station to the common medium based on the state of the authorization flag.
5. The data processing network according to claim 4, wherein said authorization flag is set to an allow access state for the station when the decrementing circuit of the time delay counter counts down to zero from a predetermined value, wherein the predetermined value corresponds to a delay time for transmission of data from the station and an additional.
6. The data processing network according to claim 4, wherein said authorization flag is set to an allow access state for the station when the decrementing circuit of the time delay counter counts down to zero from a predetermined value, wherein the predetermined value corresponds to a delay time for transmission of data from the station and an additional interval, wherein the additional interval is proportional to a duration of a most recent access time of the station to the common medium.
7. The data processing network according to claim 5, wherein the additional interval is proportional to a duration of a most recent access time of the station to the common medium.
8. The data processing network according to claim 7, wherein said processor further stores a previous count value of the collision counter and when the authorization flag is set to a no access state, said processor compares the previous count value with the number of collisions presently detected by the collision counter and if the previous count value is equal to the presently detected number of collisions, the station is allowed access to the common medium.
Description

The invention relates to a data-processing network having non-deterministic access, i.e. a network including a plurality of stations communicating with one another by accessing a common medium, using a non-deterministic protocol, i.e. a protocol that does not make it possible to predict the waiting time that will be necessary when a given station requests access to the medium at a given instant. This waiting time is referred to as the “access time” below. For example, a protocol that consists in checking that there is no carrier present on the medium, and in then starting to transmit a message while detecting any collision with another message that happens to start transmitting at the same instant, is a non-deterministic protocol. A station is incapable of predicting transmission of messages by other stations. Access time can be long if traffic on the common medium is heavy. Access time then slows down real-time applications prohibitively.

The most commonly-used common medium is a bus interconnecting all of the stations, or else a “passive hub”, i.e. a star interconnector to which each station is connected via an individual link, so that the links are equivalent to a bus going from station to station. To reduce the risk of collision, a first known solution consists in replacing the passive hub with an active hub, i.e. with routing apparatus, to which each station is connected via an individual link, and which enables the number of collisions to be reduced. It is necessary to use a cascade of hubs if the network includes a large number of stations (e.g. sixteen). That solution is therefore very costly, especially if the network is duplicated to make it more reliable.

Conventionally, each station is connected to the common medium via an interface circuit which manages the access protocol for accessing the medium. To reduce the risk of collision, a second known solution consists in modifying the implementation of the access protocol, in the interface circuit, so as to reduce the number of collisions. That solution thus consists in developing a proprietary circuit instead of using a circuit that complies with a standard and is commercially available. That solution is therefore costly.

SUMMARY OF THE INVENTION

An object of the invention is to provide a network in which access time is made deterministic by eliminating almost all risk of collision, by using means that are cheaper than those of the known solutions.

The invention provides a data-processing network having non-deterministic access but having deterministic access time, the network including a plurality of stations communicating with one another by accessing a common medium using a non-deterministic protocol, said network being characterized in that each station includes:

means for detecting whether there is a risk of collision between a plurality of stations trying to access the common medium; and

means for limiting its mean bit rate over the common medium to a predetermined maximum value at least during the periods in which there is a risk of collision between a plurality of stations trying to access the common medium, said maximum value being chosen such that the sum of the respective maximum values chosen for all of the stations is less than the mean bit rate that can be accommodated by the common medium.

A network characterized in this way encounters almost no collisions because the sum of the respective maximum values chosen for all of the stations is less than the mean bit rate that can be accommodated by the common medium.

In a preferred embodiment, the means for limiting the mean bit rate of a station comprise time-delay means authorizing a station to accesss the common medium after expiration of a delay starting at the end of the most recent access by the station, and having a duration which is proportional to the duration of said most recent access.

A network characterized in this way is less costly to implement because the time-delay means may be constituted by a portion of the software of the processor of the station. A commercially available interface circuit may be used with no modification.

In a preferred embodiment, the means for detecting whether there is a risk of collision between a plurality of stations trying to access the common medium comprise means for determining whether at least one collision has taken place since the beginning of the most recent transmission performed by the station over the common medium, and for concluding that there is a risk of collision if at least one collision has occurred since the end of the most recent transmission performed by said station.

A network characterized in this way is cheap to implement because the means for detecting whether there is a risk of collision may be implemented by using a collision counter that already exists in certain commercially available interface circuits.

The invention can be better understood and other characteristics appear from the following description and from the accompanying figures, in which:

FIG. 1 is a timing diagram showing how an embodiment of a network of the invention operates;

FIG. 2 is a block diagram summarizing this embodiment; and

FIG. 3 is a flow chart of the operations performed in this embodiment.

DESCRIPTION OF PREFERRED EMBODIMENT

The embodiment described below by way of example is a network complying with IEEE standard 802.3, sold under the Ethernet trademark, and having a medium whose mean bit rate is 100 Mbits per second.

The diagram in FIG. 1 shows a certain number of events which are seen from a given station as a function of time t:

on a first line, the content of a counter “col” indicates the number of collisions on the medium, and the count starts again from zero when it reaches its maximum value which is, for example, 65,535 (16-bit counter);

on a second line, the data frames D which are transmitted by the station in question;

on a third line, the value of a flag “aut” which authorizes the station in question to transmit a frame when it has the value 1; and

on a fourth line, the value “delay” is a time-delay counter DELAY.

At the beginning of the time interval shown in FIG. 1, the collision counter “col” has an arbitrary value. No frame is being transmitted. The flag “aut” has the value 1 which authorizes the station to transmit, and the time-delay counter DELAY has the value 0.

At an instant t0, the station needs to transmit a frame A1 over the medium. The value 1 of the flag “aut” indicates to it that it is authorized to access the medium because there is no risk or little risk of collision. It is authorized to transmit the frame A1 immediately. The frame has a length corresponding to a transmission time T1, for example. Just before transmission, the current value “coll” of the collision counter is backed up to serve as a reference in subsequently processing.

At the start of transmission of the frame A1, the time-delay counter DELAY is initialized with a value such that counting down to 0 takes a time T1+T1′. The time T1 is calculated on the basis of the length of the frame A1, and of the nominal bit rate on the common medium. The time T1 is calculated such that the value of the mean bit rate of the station during the interval T1+T1′ is equal to the maximum mean bit-rate value chosen for the station in question. In this example, the maximum mean bit-rate value of the station is chosen to be equal to one half of the nominal bit-rate of the common medium. Accordingly, the initialization value is chosen such that it counts down for a time T1+T1′ equal to twice the duration T1 of the frame A1 that the station is going to transmit. The flag “aut” is set to zero for the entire count-down time so as to prevent the station in question from occupying the common medium if there is a risk of collision. If there is no risk of collision, the station does not take into account the flag “aut”.

When it has finished transmitting the frame Al, the station ceases to transmit for a certain time T2, longer than the time T1′. During this period, the value “delay” of the counter DELAY returns to 0, at instant t1, thereby setting the value of the flag “aut” to 1 again.

Then, at instant t2, the station in question once again needs to send a frame A2 . The value 1 of the flag “aut” authorizes transmission without checking whether there is a risk of collision. The station thus transmits the frame A2 immediately. Just before transmission, the current value col2=col1 of the collision counter is backed up to serve as a reference subsequently. The counter DELAY is initialized at a value T3+T3′ such that it counts down for a time equal to twice the duration T3 of the frame A2 that the station is going to transmit. The flag “aut” is set to zero for the entire count-down time T3+T3′ so as to prevent the station in question from accessing the common medium if there is a risk of collision.

Then, the station ceases to transmit for a time T4 longer than T3′. After the end of transmission of frame A2, but during the count-down time T3+T3′, a collision is detected at instant tc1. The value “col” of the collision counter is then increased by unity. A little later, at an instant t3, the station needs to transmit a frame A3. Since the flag “aut” has the value 0, it prevents the station in question from accessing the medium unless there is no risk of collision. It must thus first determine whether there is a risk of collision. For this purpose, it compares the current value col3 of the counter “col” with the backed-up value col2. The current value col3 is equal to col2+1. Therefore, there is a risk of collision, and the station must defer its transmission until the flag “aut” takes the value 1 again.

At instant t5, the counter DELAY returns to the value 0, the flag “aut” is set to the value one again, and the station then transmits the frame A3 which has a duration T5. Just before transmission, the current value col4 of the collision counter is backed up to serve as a reference subsequently. The time-delay counter DELAY is initialized at a value such that counting down to zero takes a time T5+T5′. In this example, since the maximum mean bit-rate value of the station is chosen to be one half of the nominal bit-rate of the common medium, the initialization value is chosen such that the counter counts down for a time T5+T5′ equal to twice the duration T5 of the frame A3 that the station is going to transmit. The flag “aut” is set to zero for the entire count-down time so as to prevent the station in question from accessing the common medium if there is a risk of collision.

After the end of transmission of the frame A3 but during the count-down time T5+T5′, a collision is detected at instant tc2. The value of the collision counter “col” is then increased by unity. A little later, at instant t5′, the station needs to transmit a frame A4. Since the flag “aut” has the value 0, it prevents the station from accessing the medium, except if there is no risk of collision. It must thus first determine whether there is a risk of collision. For this purpose, it compares the current value col5 of the counter “col” with the backed-up value col4. The current value col5 is equal to col4+1. Therefore there is a risk of collision, and the station must defer its transmission until the flag “aut” takes the value 1 again. At instant t6, the flag “aut” goes to 1, transmission of frame A4 commences, the flag “aut” is reset, and the counter DELAY is re-initialized.

The maximum mean bit rate of each station may be different depending on the station. The only condition that is necessary to reduce the risk of collision is that the sum of the respective maximum values chosen for all of the stations is less than the mean bit rate that can be accommodated by the common medium.

FIG. 2 is a block diagram summarizing an embodiment of the network of the invention. It includes five analogous stations S1, S2, S3, S4, and S5 connected to a common medium M constituted by individual links for respective ones of all of the stations, and by a “passive hub” H on which said links converge. This star structure is equivalent to a bus going from station to station. In particular, two frames collide if two stations try to transmit at the same time. Each station, e.g. station S1, comprises:

a local bus BL;

a processor P comprising an input/output connected to the local bus BL, a register R for storing the flag “aut”, a queue F in which to put one or more frames that are ready to be transmitted but that cannot be transmitted immediately;

an “interchange” memory ME having an input/output connected to the local bus BL;

a conventional interruption management circuit comprising a time-delay counter DELAY having: a clock input for receiving a clock signal, and a decrementation control input and an initialization input connected respectively to two outputs of the processor P, and an output connected to an input of the processor P to supply it with an interruption signal causing it to decrement the value “delay” of the counter DELAY; and

an interface circuit CI having an input/output connected to the local bus BL, and an input/output connected to the “hub” H, and including a collision counter CC.

FIG. 3 is a flow chart showing the operations performed in this embodiment. An application makes a transmission request 1. The processor P reads 2 the value “col” of the collision counter CC. Then it tests 3 the value of the flag “aut”.

If the flag is equal to 1, the processor P successively performs the following operations:

resetting 10 the flag “aut” to 0;

starting transmission 11 of the frame to be transmitted, via the interchange memory ME, and the interface circuit CI;

backing up 12 the value “col” of the collision counter CC;

re-initializing 13 the time-delay counter DELAY to the value T+T′, where T is the time calculated for transmitting the frame which is to be transmitted, and where T′=T in this example; and

ending 9 the sequence.

If the flag is equal to 0, the processor P compares 4 the “col” value that it has just read with the preceding “col” value that it has backed up; and

if the two values are identical, the processor P performs the above-mentioned operations 10, . . . 13, and 9;

otherwise, it performs an operation 5 consisting in writing the frame to be transmitted in the queue F, and goes to the end 9 of the sequence.

Furthermore, the interruption management circuit CGI periodically supplies the processor P with an interrupt signal causing it to decrement the value “delay” of the time-delay counter DELAY until said value reaches 0. When said value reaches 0, the processor p sets the flag “aut” to 1 again, and it transmits the first of the frames that are waiting in the queue f over the medium m.

Citations de brevets
Brevet cité Date de dépôt Date de publication Déposant Titre
US4271507 *7 juin 19792 juin 1981Ford Motor CompanyCommunication broadcast channel interface
US4847835 *5 nov. 198511 juil. 1989Inria Institute National De Recherche En Informatique Et An AutomatiqueProcess and device for the transmission of messages between different stations through a location distribution network
US5047916 *24 mars 198910 sept. 1991Kabushiki Kaisha ToshibaMethod and apparatus of free space enumeration for collision avoidance
US5056107 *15 févr. 19908 oct. 1991Iris Systems Inc.Radio communication network for remote data generating stations
US5369639 *24 déc. 199029 nov. 1994Ncr CorporationLocal area network having a wireless transmission link
US5371494 *11 avr. 19946 déc. 1994Laboratoire Europeen De Recherches Electroniques AvanceesMethod for optimizing the transmission of authorization of access to a network comprising open channels
US5381413 *28 déc. 199210 janv. 1995Starlight NetworksData throttling system for a communications network
US5553072 *30 janv. 19953 sept. 1996Northrop Grumman CorporationCommunication apparatus and method
US5577069 *9 déc. 199419 nov. 1996National Semiconductor CorporationSignalling method and structure suitable for out-of-band information transfer in communication network
US5592483 *6 juin 19957 janv. 1997Sharp Kabushiki KaishaData communication apparatus achieving efficient use of the media
US56006517 avr. 19954 févr. 1997Molle; Mart L.Binary logarithmic arbitration method for carrier sense multiple access with collision detection network medium access control protocols
US5604869 *20 déc. 199518 févr. 1997Apple Computer, Inc.System and method for sending and responding to information requests in a communications network
US5625825 *21 oct. 199329 avr. 1997Lsi Logic CorporationRandom number generating apparatus for an interface unit of a carrier sense with multiple access and collision detect (CSMA/CD) ethernet data network
US5642360 *28 août 199524 juin 1997Trainin; SolomonSystem and method for improving network performance through inter frame spacing adaptation
US5661727 *12 juin 199626 août 1997International Business Machines CorporationSchemes to determine presence of hidden terminals in wireless networks environment and to switch between them
US5706274 *7 sept. 19956 janv. 1998Tetherless Access Ltd. (Tal)CSMA with dynamic persistence
US5734639 *8 mai 199631 mars 1998Stanford Telecommunications, Inc.Wireless direct sequence spread spectrum digital cellular telephone system
US5737330 *11 janv. 19967 avr. 1998Meteor Communications CorporationSystem and method for the efficient control of a radio communications network
US5774658 *17 sept. 199630 juin 1998Advanced Micro Devices, Inc.Arrangement for accessing media in a network having universal multiple access nodes and carrier sense nodes
US5784559 *6 nov. 199521 juil. 1998Sun Microsystems, Inc.Full duplex flow control for ethernet networks
US5802041 *17 sept. 19971 sept. 1998International Business Machines CorporationMonitoring ethernet lans using latency with minimum information
US5838688 *11 oct. 199617 nov. 1998Advanced Micro Devices, Inc.Determining the number of active nudes on an ethernet network by counting a number of packet receptions
US5850525 *29 mars 199615 déc. 1998Advanced Micro Devices, Inc.Method and apparatus for adding a randomized propagation delay interval to an interframe spacing in a station accessing an ethernet network
US5852723 *6 août 199622 déc. 1998Advanced Micro Devices, Inc.Method and apparatus for prioritizing traffic in half-duplex networks
US5854790 *11 juil. 199729 déc. 1998Compaq Computer Corp.To communicate data between a transmitting/receiving data device
US5896561 *23 déc. 199620 avr. 1999Intermec Ip Corp.Communication network having a dormant polling protocol
US5940399 *20 juin 199617 août 1999Mrv Communications, Inc.Methods of collision control in CSMA local area network
US5957854 *5 déc. 199728 sept. 1999Besson; MarcusWireless medical diagnosis and monitoring equipment
US5963560 *5 mars 19975 oct. 1999Advanced Micro Devices, Inc.In network stations
US5968154 *24 juil. 199619 oct. 1999Cho; Jin YoungDistributed priority arbitrating method and system in multi-point serial networks with different transmission rates
US6044396 *14 déc. 199528 mars 2000Time Warner Cable, A Division Of Time Warner Entertainment Company, L.P.Method and apparatus for utilizing the available bit rate in a constrained variable bit rate channel
US6072798 *31 oct. 19966 juin 2000Whittaker CorporationNetwork access communication switch
EP0377361A111 déc. 198911 juil. 1990THOMSON CONSUMER ELECTRONICS R&D FRANCE SNCOptimization method for the authorization release of access to a network constituted by open channels
EP0632619A228 juin 19944 janv. 1995Digital Equipment CorporationCollision reduction method for ethernet network
Citations hors brevets
Référence
1V. Y. Zagurski et al, "Random-Access Method with Deterministic Delay and Control Capability", Automatic Control and Computer Sciences, vol. 23, No. 3, Jan. 1, 1989, pp. 59-62.
Référencé par
Brevet citant Date de dépôt Date de publication Déposant Titre
US6711139 *10 avr. 200023 mars 2004Nec CorporationTransmitting and receiving apparatus for satellite communications
US729947013 sept. 200120 nov. 2007International Business Machines CorporationMethod and system for regulating communication traffic using a limiter thread
US734601010 janv. 200318 mars 2008The Boeing CompanyHybrid data bus for achieving deterministic performance for non-deterministic network bus type interfaces
US800154527 sept. 200716 août 2011International Business Machines CorporationMethod and system for regulating communication traffic using a limiter thread
Classifications
Classification aux États-Unis370/445, 709/234, 370/447, 709/235, 709/225, 709/233, 370/446, 370/448
Classification internationaleH04L12/931, H04L12/413
Classification coopérativeH04L49/351, H04L12/413
Classification européenneH04L12/413
Événements juridiques
DateCodeÉvénementDescription
17 mars 2009FPExpired due to failure to pay maintenance fee
Effective date: 20090123
23 janv. 2009LAPSLapse for failure to pay maintenance fees
4 août 2008REMIMaintenance fee reminder mailed
24 juin 2004FPAYFee payment
Year of fee payment: 4
20 juil. 1999ASAssignment
Owner name: ALCATEL, FRANCE
Free format text: CHANGE OF NAME;ASSIGNOR:ALCATEL ALSTHOM COMPAGNIE GENERALE D ELECTRICITE;REEL/FRAME:010084/0223
Effective date: 19980914
26 juin 1997ASAssignment
Owner name: ALCATEL ALSTHOM COMPAGNIE GENERALE D ELECTRICITE,
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:VAUTEY, BERNARD;REEL/FRAME:008603/0757
Effective date: 19970402